Ozone Destruction Blamed On Chlorine In Atmosphere

November 27, 1987|United Press International

WASHINGTON -- The mysterious hole in the ozone radiation shield over Antarctica is caused by a chemical reaction involving chlorine from gases used for years as propellants in spray cans, scientists confirmed on Thursday.

The chemical reaction is possible only in the presence of polar clouds, composed of tiny ice crystals, and the amount of sunlight that reaches the South Pole area in the late winter and early spring, scientists wrote.

``It`s only recently we began looking at ice particles as possible participants,`` said Mario Molina, an atmospheric chemist at the California Institute of Technology`s Jet Propulsion Laboratory in Pasadena, Calif.

The complex reaction was described in two separate papers in the journal Science by Molina and colleagues and another team at Stanford Research Institute International in Menlo Park, Calif.

Ozone is the only gas in the atmosphere that filters out harmful amounts of ultraviolet radiation from the sun.

The chlorine comes from chlorofluorocarbons, widely used as refrigerants in air conditioners and freezers, as spray-can propellants and in plastic foam insulators and containers such as those used at fast-food restaurants.

The CFC`s, as they are known, make their way into the stratosphere 6 to 30 miles high, where most of the ozone is. Ultraviolet light breaks down the chlorofluorocarbons, starting the complex reaction.

Two resulting compounds, hydrogen chloride and chlorine nitrate, normally don`t react with one another, Molina said, but in the presence of ice in the polar clouds, they form molecules of chlorine. These molecules absorb light and break apart into single chlorine atoms known as free radicals, which rapidly destroy ozone.

Molina said the reaction occurs in the early spring because of a complex interaction between light and weather patterns. The polar clouds form in winter when light reaches its minimum and wind currents isolate Antarctic air from the rest of the globe`s atmosphere.